2010 has been both the year of 3-D and the year of the “throwback,” so it’s only fitting that director Alexandre Aja’s Piranha 3D mixes the two into one B-movie splatterfest. After a sleepy lakeside Arizona town finds itself under two terrifying invasions -- first from hundreds of hard-partying Spring Breakers, then thousands of prehistoric piranhas -- it’s up to the local sheriff (Elisabeth Shue, playing decidedly against type) to keep everyone safe. An eclectic ensemble cast makes up Piranha 3D’s unlikely group of survivors as the chaos comes to a head. An unapologetically guilty-pleasure of a movie, Piranha 3D is schlocky late-summer fun that just might be the most outrageous and demented movie of the year.

With Piranha 3D, director Alexandre Aja has successfully one-upped James Cameron -- well, when it comes to the Piranha franchise at least. Well before Avatar, the Hollywood mega-director made his feature directing debut with Piranha II: The Spawning, a silly and poorly received sequel to the original Roger Corman-produced cult classic (which in turn launched the careers of Joe Dante and John Sayles). So it’s only fitting that the 3-D remake fell to Aja, a well-respected member of the horror community following his acclaimed debut High Tension and The Hills Have Eyes redo.

Better known for gritty, grisly horror than light-hearted genre fun, Aja struggles a bit maintaining the requisite horror/comedy balance throughout. While the film’s first half nails the B-movie tone with just the right mix of satire, dark humor and rapid-fire nudity and gore, some of the fun is muted when the climactic nearly half-hour beach massacre turns Saving Private Ryan-level grotesque. Still, the script mixes inventive kills, clever sight gags and enjoyable cameos as Piranha 3D manages to do what past self-aware B-movies like Snakes on a Plane couldn’t: It takes it’s gleefully demented premise of Spring Break-meets-creature feature and ably delivers on it, even if it’s not quite sure what to do with all those prehistoric piranhas after it’s let them loose.

Dedicated to the horny teenager in all of us, Piranha 3D redefines the word “gratuitous” with its record-setting T&A and violence, as Aja chums the water with fake blood by the gallon and more silicone than a plastic surgery trade show. As gory and nudity-filled as advertised, if not even more so, Piranha 3D tests the depths of its R-rating, culminating in an underwater naked ballet between pin-up girl Kelly Brook and porn star Riley Steele that’s downright artful (and knowingly tongue-in-cheek). Translation? This isn’t exactly a date movie. But moments like this are when Piranha 3D is at its best, walking that fine line between clever schlock and exploitative overkill.

Conceived from the start in 3-D but ultimately post-converted thanks to the inherent challenges of the movie’s watery setting, you can forget about an Avatar-style immersive 3-D experience. Aja coordinates a virtually non-stop parade of inventive gross-out 3-D effects, as everything that can come flying at the screen does, along with a few objects that definitely shouldn’t. Piranha 3D is far from perfect, and ends on a frustratingly underwhelming note, but for a film that aims to get as in-your-face as cinematically possible, it certainly succeeds.